Rhodesia is – was, if you prefer to use the name Zimbabwe – a small country measuring roughly 750 kilometres (or 466 miles) north to south and 850 kilometres (529 miles) west to east.

HF (High Frequency) radio is normally accepted as being for long range communications beyond the reach of conventional VHF (Very High Frequency) radio. Long range can be anything from a few hundred kilometres to halfway round the world and the construction, and type, of antenna plays a big part in HF communications.

The most common HF antenna in use – and that was used in the Rhodesian Army – is the half-wave dipole that can be erected either a T or an inverted (upside down) V configuration.

In the early 70s, probably around 1972/1973, JOC Hurricane, the operational field headquarters of Operation Hurricane and HQ 2 Brigade, moved from Centenary to the small town of Bindura.

The camp was just on the edge of the town and there were several very large trees around the grounds that provided shade to mainly the middle of the camp where the ops rooms – and officer’s messes – were located.

The radio room and other communications were housed in a long corrugated iron building just inside the boom-guarded entrance to the camp. The back of the building was towards the road and we erected our antennae on three poles in a T configuration between the building and the road.

The centre pole supported the centre point of four antennas (we used four frequencies as a rule – night frequency, day frequency and two intermediate frequencies). The outer poles were where the ends of the dipoles were supported by their halyards. The longest antenna, for the lowest frequency, was highest on the pole and the shortest, for the highest frequency, on the bottom.

The antenna each had their own feeder that ran into the radio room. Instead of having a common feed or some way of combining the feeders we marked the ends of the feeders, near the radio connector, with the relevant frequency number on a piece of tape and when we changed frequency we removed and connected the cables accordingly. 

This unsophisticated, simple but effective, setup gave us excellent communications coverage of our operational area and, had we wanted to, we could have communicated with any part of the country.

One day, probably around the 20^th of the month, we had a visit from a warrant officer who was

stationed with the signals technical squadron and;
was a radio amateur and;
was a very self-important and self-opinionated person – and also a genuinely, very clever electronics/radio technician.

Our OC at the time was also a keen radio amateur and this warrant officer swamped the OC with jargon and theory to the point that he gained permission to REORGANISE our antennas to OPTIMISE our communications. He maintained that the antennas were too close to each other – although only one was in use at any one time, not high enough and that they ought to be more spread out and not parallel to each other.

Our interfering warrant officer, having obtained carte blanche from the OC, against my ultimately ineffectual protestations, proceeded to have my men climbing trees and stringing the antennas anything from one and a half to two times as high as our little behind-the-radio-room masts. We now had this spider-web of antennas, feeder cables and halyards in the trees over the headquarters.

On questioning my exhausted operators over the next day or two after the visitor had departed, I determined that the only noticeable difference was that communications were not as good as before the rearranging of the antennas. Also more frequency changes had to be made to maintain communications.

At the end of every month we were issued a list of new frequencies to use and all antennas had to be trimmed to the new dimensions and tuned up. This involved physically changing the length of the antenna elements but now our antennas were tangled in the treetops and endangering the men trying to work with them.

I approached the OC and asked if I might speak frankly. He agreed and I asked him (probably a bit sarcastically – which he took in good part I seem to remember) if he could get Sergeant Major XX from 12 Squadron out with a team to change our antennas for us because, as he was aware, it was changeover time. I also reiterated what I had already told him – that there had been zero HF communication improvement in relation to the effort that had been required to create the spider web above our heads.

With a rueful smile the OC conceded that he had allowed the silver-haired, smooth-tongued warrant officer to mislead him, against his better judgement, in respect of our practical and functional antenna set-up. “Put it back as it was, Staff,” he told me “and apologise to the men for all the trouble”. “Thank you Sir, I replied”.

He was a really decent man, Henton Jaaback, destined to become our last Corps Commander and one of the finest I ever served with. He became a friend after our service – he was lost to us a few years ago.

The men almost cheered with gratitude and, with renewed enthusiasm, they got the antennas back to the good, practical setup we had been using. Afterwards we had rolls and rolls of co-axial feeder cable left over from the loooonnng feeder cables that had been necessary to reach the antennas in the tree canopy over the HQ. A real waste in those troubled times but I think they were recycled and eventually put to good use.

There is always a balance between theory and practical experience and the lesson taken from this is – if it ain’t broke, don’t go FIXING it.

For some information on HF antenna go to my earlier post
http://eriktheready.com/about-antennas/

This article will, of necessity, be VERY basic…

One of my favourite subjects has always been HF (High Frequency) radio communications. Because it can be fairly demanding I have found, over the years, that people do not want to be bothered with it. The antennas require knowledge to erect and maintain, some knowledge of how frequencies react at certain times of the day and, particularly in the case of mobile installations, some knowledge of the principles of earthing and potential differences. Very few people have believed in HF and if they did not have someone on hand who could look after it the installations that were put in would be neglected and the equipment blamed for all manner of reasons.

I talk about HF in several of my articles and I thought perhaps I should devote a short post to outlining some of the basics of how HF radio works – this is very basic so, all you technical types, please don’t confuse the issue with complex discussion around the subject.

HF (High Frequency) radio is normally accepted as being intended for long range communications beyond the reach of conventional VHF (Very High Frequency) radio. Long range can be anything from a few hundred kilometres to halfway round the world and the construction, and type, of antenna plays a big part in HF communications.

The most common HF antenna in use – and that was used in the Rhodesian Army – is the half-wave dipole that was normally erected in a T configuration (an inverted, upside down, V configuration can be used where a space for a normal dipole is constrained) (see graphics). I know that these antenna work exceptionally well for short and medium distance HF communication – and in some cases, properly erected, around the world.

One of the VERY BASIC antenna fundamentals we were taught on our operators’ courses was – the greater the distance you want to cover on HF the higher the antenna needs to be. Conversely an antenna that was comparatively low to the ground (as ours generally were), would tend to have a much SHORTER skip distance (bearing in mind that the area covered when the signals came back to earth was not a SPOT but actually a very large (almost) omni-directional footprint. Remember – Rhodesia has a comparatively small land area less than 900 kilometres at its widest point.

So, although with our VHF communications we were always trying to get high ground for our relay stations, the rationale in respect of HF was a bit different.

Skip distance is the distance from where the effective ground coverage (the area of direct communication over the ground from the base to an outlying station) ends and the first radio waves refracted from the ionosphere return to earth (see graphic). This is because a dipole antenna is primarily designed for long range communication and makes use of sending the signal to the ionosphere where it is refracted (bounced if you like) back to earth. The sharper the angle at which the signal reaches the ionosphere the closer to the base station it will return to earth. The reverse is true and is achieved by adjusting the height of the antenna from the ground to control the angle of the radio wave.

Think of looking into a mirror. If two people stand a metre apart in front of a mirror the angle at which they see each other is very small. If they move away from each other so as to still be able to see each other in the mirror, the angle at which they are looking into the mirror becomes greater and greater as they move further apart.

Besides the height of the antenna two other main factors affect how the radio waves react to the ionosphere. The frequency in use and the power of the transmitter. Too much power can be as bad as too little and the wrong frequency for the time of day will result in poor, or no, communications. I will resist going into too much detail and, for those who are interested, much information is available on the web. I know what I was taught by very good instructors a lifetime ago and what I have learned because I so enjoyed the subject – but it is practical stuff that I will post about in other ANTENNA articles – about my experience of the use and misuse of antenna in both the military and as a civilian!